A theory describing the deposition of monodisperse and polydisperse carbon particles onto the surface of monodisperse and polydisperse plastic spheres in simple shear flow was developed. The polydispersity of the plastic and the carbon particles was described by log normal distributions. Smoluchowski＇s equation for the collision frequency between the carbon and the plastic spheres was used. The theory involves few assumptions, the most important one being that the carbon particle occupies an area on the plastic surface equal to its projected area. Expressions were derived to calculate the orthokinetic deposition efficiency and hence the deposition rate at the early stages of the deposition phenomenon. Comparing theoretically calculated with experimentally measured values of the number of carbon particles enables calculation of the orthokinetic deposition efficiency.